Retrospective and prospective studies will be conducted to more fully define the epidemiology and natural history of viral myopericarditis. Acute and convalescent sera from patients with clinically diagnosed myopericarditis, submitted to this laboratory between 1967 and 1975 and sera from the approximately 100 new cases submitted each year, will be tested by microneutralization for a significant antibody rise and/or specific immunoglobulin (Ig) M antibody to Coxsackieviruses B1 through B5. Immunofluorescence and immunoperoxidase techniques, in conjunction with density gradient serum globulin fractionation will be investigated as a more rapid and less complex means of detecting and quantitating specific IgM antibody. The relative importance of the different Coxsackievirus B sero-types to the etiology of myopericarditis and the ratio of this entity to all Coxsackie-virus B induced disease diagnosed by this laboratory also will be studied. We will seek to establish by contacting referring physicians and patients with and without Coxsackie B associated myopericarditis some of the following data: onset data, clinical course and differences between Coxsackie B and non-Coxsackie myopericarditis, descriptive epidemiologic characteristics of the population involved, and the course subsequent to the acute episode especially in regard to the development of chronic cardiac dysfunction. Finally, we will investigate other etiologies likely to be involved in this disease. If the Coxsackie B viruses are responsible for considerable serious cardiac disease, this information would justify efforts to develop a vaccine.